The start isn't obvious at all. I will try to post the solution either tonight or tomorrow if no one else makes an attempt, but if you are woking on it, just look up Lucena position and ask yourself how you would try to reach it from the position above. The real key to understand is how to keep the white king from foiling the reaching of the Lucena position- at least then you might find the right first move a bit more easily.

This is why the old joke about all rook endings being drawn has such power.